Agriculture Reference
In-Depth Information
19
Electrical Signals in Long-Distance
Communication in Plants
Kazimierz Trebacz, Halina Dziubinska, Elzbieta Krol
Abstract
Action potentials (APs) belong to long-distance signals in plants. They fulfill the
all-or-none law, propagate without decrement and their generation is limited by refractory
periods. The ion mechanism of APs was elaborated in giant
Characean
algae and extended
by another model plant - the liverwort
Conocephalum conicum
. It consists of an increase
in cytoplasmic Ca
2+
concentration ([Ca
2+
]
cyt
) which activates anion channels responsible
for Cl
−
efflux and for membrane depolarization. Repolarization occurs after the opening
of potassium channels and K
+
efflux. The resting potential is restored by the electrogenic
proton pump. A number of ion channels which may play a role in AP were identified by
the patch-clamp technique. APs propagate on the principle of local electrical circuits. They
cover whole plants, plant organs or definite tissues, mainly phloem, phloem parenchyma
and protoxylem. APs mediate between local stimulation and movements in carnivorous
Dionaea muscipula
,
Aldrovanda vesiculosa
, and tigmonastic
Mimosa pudica
.Theroleof
APs in regulation of respiration, photosynthesis, growth, pollination, fertilization and gene
expression is well documented. An AP-coupled increase in [Ca
2+
]
cyt
seems to play a central
role in signal transduction.
19.1
Action Potentials
19.1.1
General Characteristics
Action potentials (APs) are widespread signaling phenomena, known main-
ly from excitable animal tissues comprising nerves, muscles and epithelia.
They exist in plants and fungi as well (Pickard 1973; Davies 1987). There are
several criteria that allow APs to be distinguished from other phenomena
having electrical components.
- APs can propagate with fairly constant velocity and without decrement.
- They are of all-or-none character, i.e., stimuli weaker than a certain
threshold do not evoke APs, whereas overthreshold stimuli trigger APs
of constant amplitude.
- Refractory periods: absolute and relative follow AP generation.
APs are also characterized by a regular time course, in contrast to wound-
induced variation potentials (VPs) (Fig. 19.1). In APs the fast depolarizing
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